1. Field of the Invention
This invention pertains to the field of administering powdered medicines in aerosol form, directly to the lungs through the throat or nasal passages. More particularly, the invention relates to an apparatus for aerosolizing and delivering medicines to the user and of a process of preparing these medicines so that repeated, accurate doses may be administered using the apparatus.
2. Description of the Prior Art
Beginning in the early 1970's, it was found that certain medicines could be administered in dry-powder form directly to the lungs by inhalation through the mouth or inspiration through the nose. This process allows the medicine to bypass the digestive system, and in some cases, allows smaller doses to be used to achieve the same desired results as orally ingested medicines. In other cases, it provides an administrative technique for medicines that display unacceptable side effects when taken by other methods.
Various devices that form inhalable mists of medicines have been invented and exist in the prior art. They are divided between those that form mists of liquid medicines, those that form mists of powdered medicines, and those that may be used to form mists of both liquids and powders. The physical characteristics of powdered medicines, with their particle sizes ranging from about 1 to about 100 microns (one micron equals one-thousandth of a millimeter), and more commonly from about 1 to about 5 microns, are so different from that of liquid medicines, there is rarely any similarity between the engineering requirements and the physical constructions of the two types of devices.
Typical prior art devices for handling dry medicines are shown and described in U.S. Pat. Nos. 3,507,277; 3,518,992; 3,635,219; 3,831,606; 3,971,377; and 4,147,166. Many of these devices have been commercialized, however, most of them have not found wide acceptance. For instance, most of these prior art devices use powdered medicine contained in a gelatin capsule with a separate dose contained in each capsule. These capsules are small and require some degree of manual dexterity to load and unload. A large portion of potential users of dry powdered medicines are found in the senior-citizen sector of the population and, unfortunately, this coincides with the major group of those inflicted with various forms of arthritis. With the minute size of the capsules and the requirements to load and unload them each time the nebulizer is used, they are difficult for these people to use.
Further, loading individual capsules with individual doses of powdered medicines is time-consuming and thus makes the dosage in capsule form a costly item. People who use a nebulizer during their daily routine are required to carry a large number of capsules. This could lead to breakage of some capsules and loss of the medicine contained therein. In other situations, the capsule might leak thus lowering the effective dosage of the medicine.
From a mechanical point of view, virtually all of the devices involve the use of capsules containing the medicines that are pierced along their sides by needles or other sharp objects. Thereafter, the powdered medicine is slowly withdrawn from the capsules by either partial vacuum, caused by forced inspiration by the individual, or by centrifugal force. Some of these patents indicate the extraction process requires forced inspiration for as long as two and one-half minutes. This time period would require the user to repeatedly inhale rather large volumes of air, each with a little dose of the medicine, often resulting in dizziness. In addition, any time a powder is extracted through a slit in a flexible capsule wall there is a significant question as to whether or not all the powder is totally inhaled.
Water can pass through the walls of gelatin capsules. In high humidity areas, as when carried in one's pocket, such water vapor could penetrate the capsule and cake the medicine contained therein. If caked, it is extremely unlikely that all of the medicine would be inhaled from the capsule so that the dosage between capsules would vary thus reducing the effect of the medicine.
Slow introduction of powdered medicine from the perforated capsule into the aerosolizing chamber, coupled with the airflow through the chamber, means that not all of the powder particles are present in the chamber at any one time. It has been found that self-scouring and inter-particle contact is an important feature in aerosolizing the powdered medicine. It has also now been found that these small particles have a tendency to build up in the aerosolizing chamber.
Much discussion has been made in the prior art concerning whether or not to allow the user to exhale into the device. The perforated capsules admit medicine very slowly into the inhalating airstream. In addition, many users are elderly persons or those who suffer from lung disease. These two factors often combine to render the user incapable of inhaling all of the medicine in one breath. Therefore, it is important to deal with the possibility that the user will exhale into the device. Exhaling involves a high-humidity airstream and, when it enters the inhalating device, may cause some plating of moisture on the interior walls. In other cases, moisture-laden air is blown into the aerosolizing chamber causing the powdered medicine to cake and fail to be extracted by later inhalations. Notwithstanding the attempts in the prior art to limit the introduction of exhaled moisture-laden air into the aerosolizing chamber, the fact remains that repeated exhaling into the device will inject a noticeable amount of moisture into the unit, thus causing cake buildup and loss of dosage.
Further, in devices where outside air is directly introduced into the aerosolizing chamber, exhaling into the unit while medicine is still being extracted from the capsule will cause medicine to be blown out of the air intake apertures. Indeed, one of the prior-art patents describes a typical inhalation treatment as recovering only 50 percent of the medicine dose contained in the capsule. Accordingly, the best manner in dealing with the problem of exhaling into the device is to just prevent it altogether--something not readily accomplished by the prior art.
Finally, the prior art has apparently not fully appreciated the advantages of reducing the size of large particles or agglomerated particles during use of the device. Large or agglomerated particles of medicine being heavier gather momentum during forced inhalation and impact the soft, wet tissue at the back of the throat instead of remaining in the air flow for deposit in the lungs. When this occurs, much of the medicine does not reach deep into the interior of the lungs and thus is not placed in a strategic location where it will be solvated for direct absorption through the areolar tissue into the blood stream. In more severe cases, such impact causes uncontrollable coughing and thus forces large volumes of moisture-laden air, as well as finely dispersed saliva, to be reinjected into the device thus causing the caking problems heretofore described.